The nerve supply to coracobrachialis in apes

Abstract

The origin of the nerve supply to coracobrachialis from the brachial plexus in apes was investigated in 4 arms from 4 chimpanzees, both arms of a gorilla and 4 arms from 4 gibbons. The general architecture of the brachial plexus was the same as in the human. In the apes examined, the nerves supplying this muscle could be classified into 2 groups: (1) distal branches arising from the musculocutaneous nerve, and (2) proximal branches arising in the region of the lateral cord. On the basis of their origin and course, the proximal branches were classified into 3 types, namely a deep ramus arising from the middle trunk and passing dorsal to the upper trunk, a medial ramus arising from the upper trunk in the lateral cord, and a superficial ramus arising from the ventral surface of the middle trunk or the root of the pectoral nerve. This classification also applies to branches to coracobrachialis in man. The 3 types of proximal branch often communicated with each other to supply coracobrachialis, whereas the proximal and distal branches were separated from each other spatially. This indicates that coracobrachialis possesses characteristics both of the pectoral girdle muscles and the flexor muscles of the upper arm.